Functional Fragments Of HpaG_Xooc, A Harpin From The Bacterial Rice Leaf Streak Pathogen Xanthomonas Oryzae Pv. Oryzicola, And Their Effects On Productivity And Biochemical Properties Of Green Tea

Harpin proteins from plant pathogenic bacteria can stimulate hypersensitive cell death(HCD), drought tolerance, defense responses against pathogens and insects in plants, and they can enhance plant growth as well. HpaG_Xooc, produced by Xanthomonas oryzae pv. oryzae, is a member of harpin group of proteins. The protein contains two copies of the glycine-rich motif(GRM), a characteristic of harpins, and a cysteine, which is absent in other harpins. Recently, we have identified nine functional fragments of HpaG_Xooc, a harpin protein from Xanthomonas oryzae pv. oryzicola, the pathogen that causes bacterial leaf streak in rice. Fragments HpaG_1-94, HpaG_10-42, and HpaG_62-138, which contain HpaG_Xooc regions of amino acid sequence as indicated by the number spans, exceed the parent protein in promoting growth, pathogen defense, and HCD in plants. Here we report improved productivity and biochemical properties of green tea(Camellia sinensis) in response to the fragments tested in comparison with HpaG_Xooc and an inactive protein control. Filed tests suggested that the four proteins markedly increased growth and yield of green tea, and increased leaf contents of tea catechols, a group of compounds that have relevance in prevention and treatment of human diseases. In particular, HpaG_1-94 was more active than HpaG_Xooc to expedite growth of juvenile buds and leaves used as green tea material and increase contents of catechols in processed teas. When tea shrubs were treated with HpaG_Xooc and HpaG_1-94 compared to control, green tea yields were over 39% and 55% greater, and leaf catechols were increased by more than 64% and 72%, respectively. The expression of three homologues of expansin genes, which regulate plant cell growth, and the CsCHS gene encoding a tea chalcone synthase, which critically regulates biosynthesis of catechols, were induced in germinal leaves of tea plants following treatment with HpaG_1-94 or HpaG_Xooc. Higher levels of gene expression were induced by the application of HpaG_1-94 than HpaG_Xooc. Our results suggest that the harpin protein, especially the functional fragment HpaG_1-94, can be used to effectively increase yield and improve the biochemical property of green tea, a drinking material with medical effects and serious requirement for public harmless farming and processing.